MOCVD Process PID Control System Realized In PLC

Abstract:MOCVD, Metal-organic Chemical Vapor Deposition, is a kind of vapor phase epitaxy （VPE） developed on the basis of a new type vapor phase epitaxial growth technique. With the compound semiconductor device market continues to expand, MOCVD system demand is growing. So easy to operate, simple and efficient, high-precision control systems MOCVD has become an urgent market demand.In this thesis, in the full understanding and analysis of several widely used at home and abroad MOCVD system architecture features and operation of the premise, designed based on the S7-1200Programmable controller MOCVD control system, and the pressure MOCVD system on which the proposed more accurate control methods.First, the pressure regulator for MOCVD systems require high control precision, multi-control mode, multi-control combination, the design selected programmable controller, and according to the control point analysis of possible control combinations, and from the combination of the optimal combination of filters. Then, the control system of the various branches of MOCVD system design, includes PLC control system, vacuum system, temperature control system, pressure control system.This design using the Siemens S7-1200series comes with new PLC PID₃Step module, write the reaction chamber pressure control program, the establishment of the reaction chamber pressure control system, to achieve dynamic equilibrium reaction chamber pressure, pressure control. When the system changes intake air amount, the reaction chamber pressure is able to maintain a stable control, according to the needs of users. To reduce external interference （reaction chamber intake air amount changes the reaction chamber temperature changes, and changes in vacuum pumping power） and discrete control （jog control whether the intake valve opening and closing） may cause a reaction chamber pressure fluctuations, the system uses a continuous PID control, reduces the overshoot, an increase of the stability of MOCVD reactor process control, improved uniformity of the coating obtained by the reaction, reliability, and product quality rate.